Method and apparatus for non-invasive measurement and analysis of semiconductor process parameters

ABSTRACT

A RF sensor for sensing and analyzing parameters of plasma processing. The RF sensor is provided with a plasma processing tool and an antenna for receiving RF energy radiated from the plasma processing tool. The antenna is located proximate to the plasma processing tool so as to be non-invasive. Additionally, the RF sensor may be configured for wideband reception of multiple harmonics of the RF energy that is radiated from the plasma processing tool. Further, the RF sensor may be coupled to a high pass filter and a processor for processing the received RF energy. Additionally, the antenna may be located within an enclosure with absorbers to reduce the interference experienced by the RF sensor. Additionally, a tool control may be coupled to the processor to provided to adjust and maintain various parameters of plasma processing according to the information provided by the received RF energy.

This is a continuation of International Patent Application No.PCT/US03/19038, filed Jun. 18, 2003, which is based on and claims thebenefit of U.S. Provisional Application No. 60/393,101, filed Jul. 3,2002, the entire contents of both of which are incorporated herein byreference in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to plasma process tools, moreparticularly, the present invention relates to sensing equipment fornon-invasive measurement and analysis of parameters of plasma processtools.

2. Description of Background Information

Plasma processing systems are of considerable use in materialprocessing, and in the manufacture and processing of semiconductors,integrated circuits, displays, and other electronic devices, both foretching and layer deposition on substrates, such as, for example,semiconductor wafers. Generally, the basic components of the plasmaprocessing system include a chamber in which a plasma is formed, apumping region which is connected to a vacuum port for injecting andremoving process gases, and a power source to form the plasma within thechamber. Additional components can include, a chuck for supporting awafer, and a power source to accelerate the plasma ions so the ions willstrike the wafer surface with a desired energy to etch or form a depositon the wafer. The power source used to create the plasma may also beused to accelerate the ions or different power sources can be used foreach task.

To insure an accurate wafer is produced, typically, the plasmaprocessing system is monitored using a sensor to determine the conditionof the plasma processing system. Generally, in such a system, the sensoris placed within the plasma to monitor certain parameters or in thetransmission line coupled to an electrode within the processing chamber.

SUMMARY OF THE INVENTION

The present invention provides a novel method and apparatus formeasurement and analysis of plasma process parameters.

A RF sensor for sensing parameters of plasma processing is provided witha plasma processing tool and an antenna for receiving RF energy radiatedfrom the plasma processing tool. The antenna is located proximate to theplasma processing tool so as to be non-invasive. The antenna may be abroadband mono-pole antenna.

In an aspect of the invention, a RF sensor may be located in anenclosure and the enclosure may be provided with a plurality ofabsorbers for absorbing RF energy. The enclosure can reduce the amountof interference seen by the antenna by attenuating RF energy originatingfrom another nearby source and reducing the distortion of the desired RFenergy. The absorbers reduce the backscattering of incident RF energy tothe antenna.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a RF sensor in accordance with anembodiment of the present invention;

FIG. 2 is a simplified block diagram of an antenna and processor inaccordance with an embodiment of the present invention;

FIG. 3 is a simplified block diagram of an antenna in accordance with anembodiment of the present invention;

FIG. 4 is a simplified block diagram of a plasma processing system inaccordance with an embodiment of the present invention; and

FIG. 5 is a simplified graph of expected harmonic data in accordancewith an embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention will be described in more detail below withreference to the illustrative embodiments disclosed.

FIG. 1 is an illustration of a RF sensor in accordance with anembodiment of the present invention. A plasma processing tool includes achamber 110. The plasma processing tool is generally powered by an RFpower source (not shown). RF energy 120 from the RF power source createsand maintains a plasma 130 in the chamber 110 of the plasma processingtool that is generally used in the processing of substrates. The plasmaprocessing tool can be assembled in any of a variety of knownconfigurations, all of which contain a chamber 110 where a plasma 130 ispresent for processing. Some of these configurations include, forexample, an inductively coupled plasma (ICP) source, anelectrostatically shielded radio frequency (ESRF) plasma source, atransformer coupled plasma (TCP) source, and a capacitively coupledplasma (CCP) source. Regardless of the source of the RF energy, theplasma 130 inside of the chamber 110 is excited by the RF energy that isgenerated by the RF power source. Accordingly, RF energy radiates fromthe chamber 110 at the fundamental RF frequency and at harmonics of thefundamental RF frequency. The harmonic frequencies are generated in theplasma 130. The magnitude and the phase of the harmonic frequenciesprovide information on the state of the plasma 130 and the chamber 110.For example, experiments at various power, pressure, and flow ratesindicate a high degree of correlation between the radiated energy andthe process parameters. Specifically, analysis indicates that the firstand second harmonics relate to the electron density of the plasma withbetter than a 99% match.

An antenna 140 is provided outside of the plasma chamber 110 to receivethe RF energy that is radiated from the plasma 130 and converts the RFenergy to an RF signal. In FIG. 1, antenna 140 is illustrated outside ofchamber 110. Alternatively, it can be located within chamber 110, butoutside of the processing area of plasma 130. In this configuration, theantenna has the benefit of being non-intrusive to the plasma 130 sinceinvasive sensors are known to change the process parameters. The antenna140 is coupled to a processor 150. The processor 150 receives the RFsignal from the antenna 140 and accordingly, is configured to processthe RF signal to provide the desired information on the state of theplasma. Additionally, since the fundamental frequency of the energysource may be in the order of megahertz, the antenna 140 may be abroadband, mono-pole antenna so it is capable of receiving the largebandwidth of the RF energy that is radiated. For example, an AntennaResearch Model RAM-220 can be used as a broadband mono-pole antenna.

FIG. 2 is a simplified block diagram of an antenna and processor inaccordance with an embodiment of the present invention. In theillustrated embodiment, the antenna 140 is coupled to a high pass filter210. Alternatively, antenna 140 can be coupled to another type of filtersuch as a bandreject, a bandpass, or a lowpass filter. The output of thehigh pass filter 210 is coupled to a low noise amplifier (LNA) 220 andthe amplified signal is then input to the processor 230. The high passfilter may be utilized to remove the fundamental frequency from thereceived signal since conventionally, there may not be usefulinformation contained in the fundamental frequency but rather the usefulinformation is contained within the harmonics of the RF energy. Ofcourse, data concerning the fundamental frequency can be collected byeliminating or adjusting the cut-off frequency of the high pass filter210. Typical attenuation of the signal below the cutoff of the high passfilter may be in the range of 40 dB. The LNA 220 amplifies the RF signalprovided from the high pass filter so the signals can be appropriatelyprocessed by the processor 230. Typical gains of the LNA may be in therange of 20-30 dB.

The processor 230 may be configured to support multiple inputs as shownin FIG. 2. In this case, several processes may be monitoredindependently and processed by a single processor 230. The processor 230may include an analog to digital (A/D) converter for converting thereceived analog signal into digital samples. The sampling rate of thesignal may be determined in a variety of methods. If, for example, thefundamental frequency of the RF energy was 13.56 MHz, then a bandwidthof 125 MHz would be suitable to measure 8 harmonics (the 8^(th) harmonichaving a frequency of 122.04 MHz). In this case, if the samplinginterval the AID converter is 100 ms and a frequency bin of 10 KHz ischosen, the sampling rate would be calculated as at least 250 MS/s bythe Nyquist criterion and the sample size would be 25,000.

Coupled to the processor 230 are a user interface 240, an externalcomputer 250, and a network 260. The user interface 240 can comprise avariety of known components with the purpose of allowing a user tointeract with the processor 230. For example, if the processor, aftersampling, were to perform a FFT (Fast Fourier Transform) of the sampleddata, the results could be displayed on a touch screen that would allowthe user to interface with the system. The external computer 250 canserve a variety of purposes including real time control of theprocessing parameters and the chamber 110. The network 260 serves toallow remote access to and from the processor by a user. For example,the FFT information can be made available to the external computer 250or to the network 260.

In an example of such an antenna and processor, the chamber parameterscan be characterized during a calibration state and the data collectedby the antenna 140 can be applied to a model that relates variousparameters of the chamber and plasma. For example, some of theparameters may include, electron density, assembly cleanliness, electrontemperature, and endpoint detection. The use of such a model may permitthe use of an antenna without regard to the absolute calibration of theantenna that may simplify sensor design parameters.

FIG. 3 is a simplified block diagram of an antenna in accordance with anembodiment of the present invention. The chamber 110, plasma 130,antenna 140, and processor 150 can be the same as those disclosed inFIGS. 1 and 2. The antenna 140 is placed in an enclosure 340 that isconnected to the chamber 110 via the connecting wall 310. The connectingwall 310 is designed to pass the RF energy that is radiated from theplasma 130, and may be quartz, alumina or any other suitable material.Alternatively, a hole may be provided in the connecting wall 310 toallow the RF energy to pass therethrough. Absorbers 320 and 330 areutilized to absorb the RF energy from unwanted sources as well as toreduce the distortion caused by the resonance of the enclosure 340,i.e., without the absorbers 320 and 330, the antenna may receiveunwanted resonance, distorting the signal that should be received. Ingeneral, the absorber can comprise material that absorbs energy atdiscrete or broadband frequencies.

Although shown on the back of the enclosure 340, the absorbers 320 and330 may be placed around the enclosure 340 on five of the sides (if theenclosure is considered to be a rectangular box). This arrangement forthe absorbers allows the RF energy to radiate from the plasma 130through the connecting wall 310 and in the enclosure while the absorbersare on the other five sides of the box.

In embodiments, the absorbers 320 and 330 may be chosen such thatabsorber 320 is selected to absorb the fundamental frequency andabsorber 330 is selected to absorb the first harmonic. A quarter wavearrangement can provide the maximum attenuation of the selectedfrequencies. Additionally, additional absorbing layers can be utilizedas desired. Although specific arrangements of absorbers have beendescribed above, any configuration of absorbers that reduce unwantedinterference may be utilized.

FIG. 4 is a simplified block diagram of a plasma processing system inaccordance with an embodiment of the present invention. For the purposeof description, the chamber 110 is shown as a capacitively coupledchamber with upper electrode 125, however, any type of system could besimilarly utilized. The plasma 130, the antenna 140 and the processor150 can be the same as described above. As previously described, theplasma 130 is excited by a RF generator 420. The RF generator 420 may bedirectly coupled to the chamber 110 or, as shown in FIG. 4, coupled tothe chamber 110 via a match network 410 or 440. In FIG. 4, two RFgenerators are shown for the purpose of illustration, however, it may bepossible to utilize a single RF Generator 420 depending on theconfiguration of the chamber 110. The Upper ELectrode (UEL) matchnetwork 410 is coupled to the upper electrode 125 and the LowerELectrode (LEL) match network 440 is coupled to the lower electrode 450.The plasma 130 is excited by the RF generator(s) 420. Accordingly, theplasma 130 radiates RF energy at a fundamental frequency and atharmonics of the fundamental frequency. The RF energy is radiated out ofthe chamber 110 and is received by antenna 140, which is locatedexterior of the plasma 130. The antenna 140 is coupled to a processor150, which has been described, in part, earlier. As described withrespect to FIG. 1, the above-described arrangement provides anon-invasive method of receiving plasma processing parameters.

The processor 150 receives the RF energy and converts the analog signalto a digital signal via an analog to digital (AID) converter. Typically,the sampling rate of the analog signal depends on the bandwidth ofinterest (i.e., the bandwidth is a function of the fundamental frequencyand the harmonics of interest). For example, a 500 MHz bandwidth maytypically be sampled at a rate of 1 billion samples per second. Ofcourse, the sampling rate can be determined as desired and should not belimited to the example above. The magnitude and the phase of the RFenergy, including the harmonics, may provide information about the stateof the plasma 130 and accordingly on the state of the chamber 1 10. Thedata may then be processed by the processor 150 and operations such as aFast Fourier Transform (FFT) and a Principle Component Analysis (PCA)can typically be used to gather information from the RF signal. Theinformation that is acquired by the processor 150 can provide insightinto parameters such as assembly cleanliness, plasma density, electrontemperature, and endpoint detection.

In one embodiment of the processor, trace data of the received RF energycan be converted into a frequency domain output signal by usingconventional techniques including the FFT. The information at theharmonic frequencies can then be extracted and multiplied bycoefficients which are obtained during a calibration of the plasmaprocessing system and determined by PCA. PCA may be useful fordetermining the coefficients because it allows a large set of correlatedvalues to be converted to a smaller set of principal values. Thereduction in the size of the set can be achieved be converting theoriginal set of values into a new set of uncorrelated linearcombinations of the original (larger) set.

Using the magnitude of the fundamental frequency and the harmonicfrequencies of the received RF energy, it is possible to perform severaldifferent analyses including, power analysis, flow analysis, andpressure analysis. By processing the information obtained from themagnitude values, it is further possible to determine between which ofthe harmonics, the largest correlation exists and as a result, determineacceptable coefficients for each frequency component. Dependenceanalysis is also possible to determine if changes in one parametereffect other parameters in the system, however, initial results indicatethat the parameters may be adjusted independently.

Further, endpoint detection may be possible from an analysis of thetrace data. Once plotted, it becomes apparent that there is asignificant shift in a harmonic of the received RF energy. Moreparticularly, it is possible that the major harmonic contribution maychange at the time of process completion.

For example, as shown in FIG. 5 which illustrates simplified, expecteddata, a change in the 3^(rd) harmonic is apparent at T1 an a change inboth the fundamental an 3^(rd) harmonic is apparent at T2. Analysis ofthe process indicates that these changes are due to completion of theprocess. Such a method of endpoint detection may be an accurate and costeffective method of endpoint detection.

The processed data is then sent to a tool control 430. The tool control430 may be configured to perform several tasks. Some of the tasks thatthe tool control 430 can perform include end point determination, powercontrol, and gas control (flow, pressure, etc.). As shown in FIG. 4, thetool control 430 is coupled to the chamber 110, and the RF generators420. In this manner, it is possible for the tool control to adjustparameters of these devices according to the data that is received fromprocessor 150 so that a repeatable process can be maintained within thechamber 110.

As described above, PCA is a multivariate statistical procedure thatpermits a large set of correlated variables to be reduced to a smallerset of principal components. Therefore, during a calibration phase, PCAcan be utilized to first generate a covariance matrix from a data setcomprising the data of various harmonics. Next, an eigensolution can beobtained from the covariance matrix and accordingly a set ofeigenvectors can be calculated. From the eigensolution, the percentagecontribution of each principal component can be calculated. Using thepercentages, coefficients can be selected accordingly by a weighted sumof the eigenvector with the percentages obtained. This calculation canbe performed for various parameters including, power, gas flow, andchamber pressure. Once the calibration is complete and the variouscoefficients are determined, the tool control can utilize theinformation in control loops as would be apparent to an individualskilled in the art. In this type of a feed back loop a reproducibleprocess may be maintained.

The processor 150 may be coupled to several devices as shown in FIG. 2.Some of the devices that are of importance in the present embodimentinclude the user interface 240 and the external computer 250.Additionally, it is possible that both the user interface 240 and theexternal computer 250 are a single device, for example, a personalcomputer.

Lastly, as can be appreciated by an individual skilled in the art, theamount of data that is processed by the processor 150 may besignificantly large. To this regard, it may be required that an externalstorage device (not shown) be utilized. One possible configuration forconnecting the storage device may be directly to the processor 150.Alternatively, it may be beneficial to use the remote storage via thenetwork 260 (shown in FIG. 2). However, any method of storing the datais acceptable. One benefit of storing the data is for future processingand analysis. Additionally, the archived data can be utilized to modelan acceptable control system for operating the tool control 430 and,accordingly, control the plasma processing.

The foregoing presentation of the described embodiments is provided toenable any person skilled in the art to utilize the present invention.Various modifications to these embodiments are possible and the genericprinciple of a RF sensor for measurement of semiconductor processparameters presented herein may be applied to other embodiments as well.Thus, the present invention is not intended to be limited to theembodiments shown above, but rather to be accorded the widest scopeconsistent with the principles and novelty of the features disclosed inany fashion herein.

1. A system for sensing parameters of plasma processing, said systemcomprising: a plasma processing tool; an enclosure placed proximate tosaid plasma processing tool; an antenna, located inside said enclosure,for receiving RF energy radiated from said plasma processing tool; and aprocessor coupled to said antenna for processing said RF energy receivedby said antenna.
 2. The system of claim 1, wherein said enclosure isattached to said plasma processing tool.
 3. The system of claim 1,further comprising: at least one absorber provided with said enclosurefor absorbing RF energy.
 4. The system of claim 3, wherein saidenclosure has at least one surface adjacent to a surface of said plasmaprocessing tool, and said at least one surface and said surface of saidplasma processing tool are configured to pass RF energy.
 5. The systemof claim 1, wherein said enclosure and said tool are adjacent and definean opening therebetween.
 6. The system of claim 4, wherein said at leastone absorber is located to prevent absorption of RF energy passingthrough said at least one surface of said enclosure adjacent to saidplasma processing tool.
 7. The system of claim 3, wherein a firstabsorber is configured to absorb a fundamental frequency of said RFenergy and a second absorber is configured to absorb a harmonicfrequency of said RF energy.
 8. The system of claim 3, wherein saidenclosure is rectangular and said absorbers are provided on all sides ofsaid enclosure except a side located proximate to said plasma processingtool.